Exhaust nozzle

Abstract

There is disclosed an exhaust nozzle for a gas turbine engine. The exhaust nozzle comprises a frame extending along a longitudinal axis, and a convergent petal pivotably attached at a convergent pivot point to the frame and extending axially downstream and radially inward from the frame. The exhaust nozzle comprises a follower roller fixed to the convergent petal on a radially outer side of the convergent petal, and a cam defining a working surface configured to engage the follower roller to react a force from the convergent petal. The cam is movable along a travel in an axial direction to actuate radial movement of the follower roller to pivot the convergent petal. The cam defines a convex working surface such that a contact angle between the follower roller and the cam varies along the travel to thereby vary an axial component of the force reacted by the cam.

What is claimed is: 
     
       1. An exhaust nozzle for a gas turbine engine, the exhaust nozzle comprising a frame extending along a longitudinal axis and the exhaust nozzle comprising:
 a convergent petal pivotably attached at a convergent pivot point to the frame and extending axially downstream and radially inward from the frame; 
 a follower roller fixed to the convergent petal on a radially outer side of the convergent petal; and 
 a cam defining a working surface configured to engage the follower roller to react a force from the convergent petal; 
 wherein the cam is movable along a travel in an axial direction to actuate radial movement of the follower roller to pivot the convergent petal, wherein the cam defines a convex working surface in which a radius of curvature of the cam is located radially outward of the cam, with respect to the longitudinal axis such that a contact angle between the follower roller and the cam varies along the travel to thereby vary an axial component of the force reacted by the cam. 
 
     
     
       2. The exhaust nozzle according to  claim 1 , further comprising a divergent petal pivotably attached at a divergent pivot point to a downstream end of the convergent petal, the divergent petal extending axially downstream and radially outward from the divergent pivot point. 
     
     
       3. The exhaust nozzle according to  claim 2 , wherein the divergent petal is connected to the frame by a linkage such that the frame, convergent petal, divergent petal and linkage form a four-bar linkage. 
     
     
       4. The exhaust nozzle according to  claim 3 , wherein the linkage is a thrust linkage which is actuatable to change length. 
     
     
       5. The exhaust nozzle according to  claim 2 , wherein the convergent petal defines a chord length from the convergent pivot point to the divergent pivot point, and wherein the follower roller is fixed between 40-80% along the chord length of the convergent petal from the convergent pivot point. 
     
     
       6. The exhaust nozzle according to  claim 1 , wherein the cam is moveable between a contracted position in which the cam is in a furthest upstream position and an expanded position in which the cam is in a furthest downstream position, and wherein the cam is configured so that a contact angle between the cam and the follower roller in the contracted position is between 80-100 degrees from the longitudinal axis. 
     
     
       7. The exhaust nozzle according to  claim 1 , wherein a ratio of a radius of the follower roller to an average radius of curvature of the cam is 0.05 or above. 
     
     
       8. The exhaust nozzle according to  claim 1 , wherein a ratio of a radius of the follower roller to a maximum radius of curvature of the cam is 0.2 or below. 
     
     
       9. The exhaust nozzle according to  claim 1 , further comprising a plurality of convergent petals angularly distributed around the exhaust nozzle, each comprising respective rollers, and the exhaust nozzle comprising a corresponding plurality of cams circumferentially spaced around the exhaust nozzle and configured to maintain engagement with a respective roller. 
     
     
       10. The exhaust nozzle according to  claim 9 , wherein the cam is fixed to a unison ring, and wherein the axial movement of the cam is actuated by axial movement of the unison ring. 
     
     
       11. The exhaust nozzle according to  claim 10 , wherein there are a plurality of divergent petals corresponding to the plurality of convergent petals. 
     
     
       12. A gas turbine engine comprising an exhaust nozzle according to  claim 1 . 
     
     
       13. An exhaust nozzle for a gas turbine engine, the exhaust nozzle comprising a frame extending along a longitudinal axis and the exhaust nozzle comprising:
 a convergent petal pivotably attached at a convergent pivot point to the frame and extending axially downstream and radially inward from the frame; 
 a follower roller fixed to the convergent petal on a radially outer side of the convergent petal; and 
 a cam defining a working surface configured to engage the follower roller to react a force from the convergent petal; 
 wherein the cam is movable along a travel in an axial direction to actuate radial movement of the follower roller to pivot the convergent petal, wherein the cam defines a convex working surface such that a contact angle between the follower roller and the cam varies along the travel to thereby vary an axial component of the force reacted by the cam, and 
 wherein a ratio of a radius of the follower roller to an average radius of curvature of the cam is 0.05 or above. 
 
     
     
       14. An exhaust nozzle for a gas turbine engine, the exhaust nozzle comprising a frame extending along a longitudinal axis and the exhaust nozzle comprising:
 a convergent petal pivotably attached at a convergent pivot point to the frame and extending axially downstream and radially inward from the frame; 
 a follower roller fixed to the convergent petal on a radially outer side of the convergent petal; and 
 a cam defining a working surface configured to engage the follower roller to react a force from the convergent petal; 
 wherein the cam is movable along a travel in an axial direction to actuate radial movement of the follower roller to pivot the convergent petal, wherein the cam defines a convex working surface such that a contact angle between the follower roller and the cam varies along the travel to thereby vary an axial component of the force reacted by the cam, and 
 wherein a ratio of a radius of the follower roller to a maximum radius of curvature of the cam is 0.2 or below.